1. Field of the Invention
This invention relates to high frequency coplanar waveguide circuit structures, and in particular to flip mounting of an integrated circuit on a coplanar waveguide having ground conductors coupled together under the flip-mounted circuit.
2. Related Art
Mounting integrated circuit flip-chips on a motherboard has been found to be an effective way to connect radio frequency circuit components together. The use of flip mounting provides a substitute attachment method that replaces the use of bond wires, backside metalization and vias, air bridges, and dielectric crossovers on the mother substrate. The conducting columns or bumps that connect the chip to the mother board can be formed using solder, brazing material or conductive adhesives. However, the preferred method is by thermocompression bonding because of the resulting reduced impact on losses and parasitic and improved consistency.
Also, in such high frequency applications, the use of coplanar transmission lines is well established. Typical examples include conventional coplanar waveguides (ground-signal-ground lines), slot lines, balanced ground-signal-signal-ground lines, and parallel-strip balanced lines. Coplanar waveguides are particularly useful because of the simplified structure provided by having both signal and ground conductors on a single plane and the resulting access to the ground planes on both sides of the signal conductor. Adjacent coplanar waveguides are known to be used to connect different flip-mounted circuits. The coplanar waveguides also provide improved isolation between signal conductors as compared to some other transmission line structures.
The flip-chip itself typically contains one or more transistors. In a power chip, a plurality of transistors are often driven by a single control lead, such as the base or gate depending on the type of transistor involved. Correspondingly, the associated set of collectors or drains, i.e., current-carrying terminals, are joined to a single output terminal. Impedance-matching for the composite power transistor is accomplished on the mother board.